Sex-biased herbivory is a potential mechanism for maintaining female-biased sex ratios in Arctic and alpine willows, which are consumed by taxonomically diverse herbivores. Differences in feeding preferences of these herbivores may determine synergistic or antagonistic pressures on populations of their shared food plants. We investigated the foraging preferences of two alpine herbivores, a caterpillar and a small mammal, both feeding on the widespread, dioecious tundra shrub Salix arctica, at different times of the growing season. The caterpillars of the Arctic moth Gynaephora groenlandica beringiana are active in the early summer, while collared pikas Ochotona collaris are most active later in the summer. We used cafeteria-type experiments to evaluate preferences for male and female leaves of S. arctica and found that the two herbivores showed different patterns in their feeding preferences. Caterpillars preferred male plants in early summer, feeding on male leaves nearly twice as much as female leaves, while collared pikas showed no preference between undamaged male and female S. arctica leaves later in the season. Sex-biased herbivory by sequential, co-occurring herbivores may have consequences for the population dynamics of dioecious plants. The cumulative effects of these different herbivores on plant population dynamics should be considered in highly seasonal environments, particularly if the relative balance of caterpillar and pika herbivory changes in the future.